A STUDY ON THE LITTERFALL AND SOIL FERTILITY OF THE DIFFERENT PLANTED FORESTS IN GUANGXI APPROACHING TO THE DEVELOPMENT OF PLANTED FORESTS AND ESTABLISHMENT OF FOREST PLANTATION INDUSTRY Infiltrability of muddy water and universal model for both muddy water and tap water in planted forest site Distribution characteristics of effective root density in the planted Robinia pseudoacacia and Platycladus orientalis forest site Soil fertility evaluation of planted forest land on the hilly-gullied Loess Plateau